1. Field of the Invention
The present invention relates to a grinding machine with a steady rest wherein in response to a signal issued from a sizing device when a workpiece being ground reaches a predetermined size, the infeed movement of a grinding wheel carrier is stopped and instead, the feed movement of a jaw of the steady rest is initiated to press the workpiece upon a grinding wheel.
2. Discussion of the Prior Art
In a grinding machine having a steady rest, a signal AS2 is issued from a sizing device when a cylindrical workpiece is ground to a predetermined intermediate size, as shown in FIG. 6. In response to the signal AS2, the infeed movement of a grinding wheel is halted and instead, a jaw of the steady rest is advanced toward the grinding wheel so as to cause the workpiece to be ground by the grinding wheel. Then, the infeed movement of the grinding wheel is resumed to grind the workpiece to a predetermined finish size.
However, in the case where there is used a grinding wheel made of cubic boron nitride, the flexing amount that the workpiece has when the feed movement of the rest jaw is initiated varies largely because the grinding wheel has a peculiar property that its grinding capability is small right after the truing, but is improved as the stock removal thereby increases. Thus, a longer grinding cycle time is required to secure a desired roundness on the finish workpieces.
More specifically, at the stage that the grinding wheel has a small grinding capability right after each truing thereon, the workpiece W has been flexed a large amount (.delta.1) toward the rest jaw T when the sizing device issues a signal representing the grinding of the workpiece to an intermediate set size DAS, as shown in FIG. 7(a). When the rest jaw T is advanced thereafter, the workpiece W is returned by its spring-back motion toward the grinding wheel G at the early stage of such advance movement of the rest jaw, whereby it is ground to be diminished by (d), as shown in FIG. 7(a). Therefore, in order that a desired roundness can be secured after the grinding caused by the spring-back motion of the workpiece W and that an allowance (L1) can be left which is necessary for the subsequent grinding by the feed of the rest jaw T and for the later fine grinding by the re-infeed of the grinding wheel G, the signal AS2 from the sizing device has to be issued earlier taking into consideration the allowance (d) ground upon the spring-back motion of the workpiece W.
However, if such is done, the following drawback occurs. That is, when the grinding capability of the wheel G is improved, the flexing amount (.delta.) the workpiece W has upon issuance of the sizing signal AS2 decreases from (.delta.1) to (.delta.2), as shown in FIG. 7(b), and the allowance ground by the spring-back motion of the workpiece W also decreases from (d) to (d'). As a consequence, the allowance which is to be ground by the feed of the rest jaw T increases from (L1) to (L2), thereby resulting in a longer machining cycle time and hence, in the degradation of productivity.